1. Field
Aspects of the present disclosure generally relate to wireless communication and, more particularly, downlink flow control based on limitations at a user equipment (UE).
2. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) systems, and Orthogonal Frequency Division Multiple Access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. The forward communication link and the reverse communication link may be established via a single-input single-output, multiple-input single-output or a multiple-input multiple-output system.
A wireless multiple-access communication system can support a time division duplex (TDD) and frequency division duplex (FDD) systems. In a TDD system, the forward and reverse link transmissions are on the same frequency region so that the reciprocity principle allows the estimation of the forward link channel from the reverse link channel. This enables the access point to extract transmit beamforming gain on the forward link when multiple antennas are available at the access point.
The 3GPP LTE represents a major advance in cellular technology and it is a next step forward in cellular 3rd generation (3G) services as a natural evolution of Global System for Mobile Communications (GSM) and Universal Mobile Telecommunications System (UMTS). The LTE provides for an uplink speed of up to 75 megabits per second (Mbps) and a downlink speed of up to 300 Mbps, and brings many technical benefits to cellular networks. The LTE is designed to meet carrier needs for high-speed data and media transport as well as high-capacity voice support. The bandwidth may be scalable from 1.25 MHz to 20 MHz. This suits the requirements of different network operators that have different bandwidth allocations, and also allows operators to provide different services based on spectrum. The LTE is also expected to improve spectral efficiency in 3G networks, allowing carriers to provide more data and voice services over a given bandwidth.
Physical layer (PHY) of the LTE standard is a highly efficient means of conveying both data and control information between an enhanced base station (eNodeB) and mobile user equipment (UE). The LTE PHY employs advanced technologies that are new to cellular applications. These include Orthogonal Frequency Division Multiplexing (OFDM) and Multiple Input Multiple Output (MIMO) data transmission. In addition, the LTE PHY uses OFDMA on the downlink and Single Carrier-Frequency Division Multiple Access (SC-FDMA) on the uplink. OFDMA allows data to be directed to or from multiple users on a subcarrier-by-subcarrier basis for a specified number of symbol periods.
3GPP LTE Release 8 specifications provide a set of frequency bands on which an LTE system can be deployed. The usage of bands can vary from country to country based on prevalent frequency allocation policies. Within a band, an actual carrier frequency being utilized can also vary from one service provider to another. The 3GPP USIM (UMTS Subscriber Identity Module) may only provide a list of PLMN IDs (Public Land Mobile Network Identifications), which may comprise a 3-bit Mobile Country Code (MCC) and a 3-bit Network Color Code (NCC). However, the PLMN ID may not provide an indication about a band to be used, and, also, it may not comprise information about a specific carrier frequency on which a desired service provider exists. User equipment (UE) operating in the LTE system may be supposed to learn and maintain an adaptive list of carrier frequencies and band information as it successfully acquires services in various countries and service providers. Hence, the UE may be required to always perform a frequency scan when attempting initial acquisition.